Gray iron castings



Patented July 18, 1950 2,515,822 4 GRAY IRON CASTINGS Lester C. Crome,West Alexandria, Ohio, assignor I to The Dayton Malleable Iron Company,Dayton, Ohio, a. corporation of Ohio No Drawing.

Application November 30, 1946,

Serial No. 713,397

6 Claims. 1

This invention relates to gray iron castings and to methods of producingthe same.

In producing gray cast iron in accordance with practices heretofore incommon use, difflculty has been encountered, especially in castingshapes having corners, projections, and the like, because of thetendency of the gray iron to chill in such regions with resultingproduction of hard corners which presented difiiculties in machining.For example, a particular clutch ring required in large quantitiesconsists of an annular disc havin a number of integral projectionsextending outward from one face of the disc. The projections normallyhave rather sharp corners and, when the ring was cast from gray iron inthe usual way, these corners often chilled and could not be machinedproperly because of the hard, brittle and generally nonuniformcharacteristics of the chilled metal.

Also, ordinary gray iron castings normally contain considerable amountsof free ferrite, e. g., ferrite in addition to that which is present asa constituent of pearlite likewise normally found in gray irons, andthis free ferrite has further contributed to machining difficultiesbecause of its tendency to foul the machine tool.

The tendency of the iron to chill can be reduced by using a softer grayiron mix, such as a mix containin an increased amount of silicon orother graphitizing agent, such as lithium, zirconium, aluminum ortitanium, and it is the general practice in the industry to adjust thesilicon content to produce a casting free of chilled hard corners oredges. While this expedient may be effective in avoiding or minimizingthe formation of hard corners, at the same time, it tends to increasethe ferrite content of the iron and, as a consequence, lowers materiallythe Brinell hardness of the product. In the case of many products, suchas the clutch ring hereinabove described, however, servicespecifications require high Brinell hardness values as well as goodmachineability and this has presented conflicting requirements diflicultof attainment by the previous practices in the art.

Furthermore, the metallic matrix of conventional gray iron usually lacksuniformity of structure even outside the chilled regions and, for thisadditional reason, does not machine with full satisfaction.

It is accordingly a principal object of the invention to so modify thecharacteristics and properties of ordinary gray irons as to provideimproved gray iron castings exhibiting the qualities of substantialabsence of hard chilled regions and resulting improved machineabilitycombined with high Brinell hardness values.

A further object is to provide gray iron castings exhibiting moreuniform matrix structures which may be machined more satisfactorily thanordinary gray iron castings.

Another object is to so modify the composition of a conventional grayiron mix as to produce therefrom, after casting the mix in the usualway, a gray iron casting of substantially reduced chill withoutobjectionable sacrifice of hardness.

It is also an object of the invention to provide simple, economical anddependable methods of producing gray iron castings exhibiting suchimproved characteristics.

Other objects and advantages of the invention will become evident fromthe following description taken in conjunction with the appended claims.

In producing gray iron castings in accordance with the presentinvention, the desirable freedom from hard corners is retained and, inaddition, the undesirable lowering of hardness normally resulting froman increased silicon content is avoided and a final product is obtainedwhich has the combined advantages of such freedom from hard cornerstogether with a maintained or, if desired, increased hardness as may bedesirable in any particular instance.

This is accomplished, in accordance with the invention, by preparing aconventional gray iron mix containin the usual constituents of such amix including a raphitizing agent, in accordance with the generalpractice hereinabove referred to, in an amount which normally wouldproduce a casting free of hard corners but exhibiting undesirably lowhardness and undesirably high content of ferrite, and then incorporatingin the mix, while it is in a molten condition and prior to pouring, asmall amount of a modifying or addition agent which has the property ofcounteracting or off-setting the undesirable effects of the graphitizingagent and stabilizing the eutectoid carbides of the mix during theperiod in which they would otherwise be subject to decomposition withaccompanying production of free ferrite. Addition of such modifyingagent inhibits and, it is believed, substantially prevents suchdecomposition and provides for stabilizing up to substantially theentire matrix in the form of pearlite to produce a casting in which thematrix is more uniform and consists predominantly of the pearliticeutectoid mixture of ferrite and cementite and contains substantially nofree ferrite, thus making it possible to secure a Brinell hardnesscorresponding to such highly pearlitic matrix formation while stillavoiding hard chilled regions. Addition of lesser amounts of modifyingagent provides intermediate controlling eifects of the same character.

As is well. known, when gray iron mixes are cooled from a molten to asolid condition, as when such compositions are cast in an ordinary sandmold, they undergo a series of transformations including the formationof eutectoid care bides initially consisting principally of. austenitefollowed by transformation of the austenite into other eutectoidcarbides such as martensite,. pearlite and the like and, finally, in theusual case, with th production of a solid castiron containing a mixtureof pearlite, flakes of graphitic carbon, perhaps some free cementite,and substantial amounts of free ferrite. In the present invention,however, the series of decompositions are inhibited in the later stagesby stabilizing the pearlitic eutectoid against further decomposition sothat, production of free ferrite is substantially avoidedand a matrixconsisting essentially of pearlite of highly uniform structure isproduced.

In practical effect, agray, iron. casting, of lower chi l and free ofhardfcorners is obtained without. lowering the Brinellfihardness and,ifdesired, the Brinell hardness may in factv be increased substantiallywhile still. avoidingv hard, chilled corners. Notwithstanding. suchincreased hardness, the castings of th present inventionv may bemachined-with considerably greater easeand uniformity because of theabsence of free ferrite and the resulting freedom from its usual foulingeffect on the machine toolas. well asth'e greater uniformity ofthematrix structure itself.

A preferred modifying agent for addition. to the gray iron mix inaccordance with the present invention comprises. antimony which may. beadded. to the molten mix eitherin th form of an alloy with another metalor in the .formof antimony alone, such as the lumnantimony'available.commercially. only. small amounts. of an-. timony are required toachieve the improved results described anditsbeneficial effects persistthrough the course of several successive castings and remeltings of the.modified iron mix.

Thus it has. been found that the addition to a usual gray. iron mix,prior to pouring, of av small percentage of the order of 0.05% ofantimony based on. the total weightof the iron. mix is sufficient. tobring about the .marked improvements hereinabove described. Largeramounts. of antimony may, be. added if desired, but as, the amount ofantimony. is increased. the iron tends to become more.brittle and. it.will usually not befound desirable to .addmore. than about 0.10% ofantimony. Smaller amounts also may be added with somewhat decreasedeffect in the lower ranges andit will. ordinarily be desirable to use.effective amountsfrom 0.01% to 0.05%, about 0.04 to.0.05%. beingpreferred for-regular foundry practice.

The antimony may be addedmost conveniently by placing the requisiteamount of lump antimony in the bottom of.a ladle and then running in themolten iron mix although the antimony also may be added afterithe ladlehas been filled, or otherwise, prior. to the actual pouring of themetal.

Gray iron mixtures customarily aretapped at temperatures of 2700-2800 F.and' may cool down to temperatures of from 2400 to 2600 F. in the ladle,depending primarily upon the weight of casting being poured which inturn largely determines the time interval during which the molten ironmix will remain in the ladle. Since metallic antimony boils at 2624" FL,some loss of this material from the molten iron is to be expected andwhite vapors, believed to be vapors of antimony, have been observedcoming off when antimony is placed in the bottom of a ladle hot from aprevious pouring or when it is added to a ladle full of molten metal.Because of the difficulty of accurate analysis, no precise determinationhas been made of the amount of antimony lost'but it is estimated that asmuch as half may be lost by vaporization when 0.05% is added whileconsiderably less than half the antimony would probably be lost if asmaller amount of the order of 0.01% were added.

It has also been found that such loss of antimony by vaporization may bereduced or, at least, that correspondingly-improved properties in theironmay be secured with somewhat lesser amounts of antimony 'if it isadded in the form of arr-alloy with another suitable non-ferrous metalsuch ascopper orlead which can be alloyed wit'h antimony and Which doesnot itself have any substantial deleterious eifect in the iron mix; Forexample; alloys of 10% antimony with 90 of either lead or copper and 20%antimony with of-either lead or copper will be foundquite suitable foraddition to the molten iron in the same way lump'antimony is added as'hereinabove described. The relative proportions ofthe alloyconstituents are not critical insofar as the presentinvention isconcerned, the only requisite being that the alloy contain an effectiveamount of antimony falling generally within the ranges hereinaboveindicated. Ordinarily, however, smaller amounts of antimony in the lowerportions of the indicated ranges, and perhaps as much as half the amountotherwise required, will be found adequately effective when added in-theform of an alloy, either because less antimony is then lost byevaporation or because of some synergistic efiect-not yetunderstood.

Notwithstanding possible loss of substantial portions of the addedantimony by evaporation, its beneficial eifects persistthrough aseries-of several castings and remeltings of themix, indicating eitherthat'an effective amount of antimony remains in the mix; as such; orperhaps that the antimonyenters into-chemicalcombination with-some ofthe other ingredients to produce a new antimony-containing agent stableunder casting temperaturesandeffective to produce the desired results.-

Specific: examples of gray-iron compositions modified by the addition;of antimony. in: accord-. ance with'the invention will nowbe set out,the amounts of antimony in each instance indicating the amount actuallyadded to the molten iron mi-x and-not necessarily. the amountpersistingin the finished'cast iron:

Example 1,

Constituent: 7 Percent Silicon 2.90 Sulfur 0.125 Phosphorous 0.130Manganese 0:60 Carbon 3.45" Antimony 0.05 Iron Balance Example 2Constituent: Percent Silicon -1 2.60 Sulfur 0.135 Phosphorous a 0.130Manganese 0.65

Carbon 3.40

Antimony 0.04 Iron Balance When prepared in the manner described andcast in the usual way in sand molds, each of the foregoing compositionswill produce a high quality gray iron shape having a matrix of highlyuniform structure consisting essentially of pearlits and containingsubstantially no free ferrite, the all-pearlitic matrix and the greatlyincreased uniformity of matrix structure being readily apparent whenprepared surfaces of the castings are examined under a microscope in themanner well understood in the art and compared with similar castingsmade in the same way but for omission of the antimony. Undesirable chilland hard corners are substantially completely avoided but the Brinellhardness will be substantially higher than would be the case if theantimony were omitted. In utilizing the invention in the casting of theparticular clutch ring previously mentioned, the resulting product wasfound to machine satisfactorily, even at the sharp corners of theupstanding projections, and the Brinell hardness was increased to valuesranging from 200 to 235 instead of values ranging from 179 to 200 whichnormally are obtained with similar gray iron mixes without addition ofantimony or similar modifying agents.

While the processes and products herein described constitute preferredembodiments of the invention, it is to be understood that the inventionis not limited to these precise processes and products, and that changesmay be made therein without departing from the scope of the inventionwhich is defined in the appended claims.

What is claimed is:

1. A gray iron casting of such composition, size and configuration asnormally .to be substantially free of chilled hard regions difficult tomachine satisfactorily and to have a Brinell hardness of the order of179-200, said casting containing appreciable amounts of carbon in flakeform and having a metallic matrix of great uniformity consistingpredominately of pearlite to the substantial exclusion of free ferriteand containing as an essential constituent a small amount of antimony ofthe order of 0.01% to 0.10%, said casting being substantially free ofchilled hard regions, and exhibiting a Brinell hardness of the order of200-235.

2. A gray iron casting containing appreciable amounts of primarygraphitic carbon in flake form and in which the metallic matrix consistspredominately of pearlite to the substantial exclusion of free ferriteand which contains antimony as an essential constituent in an amount notexceeding about 0.10%.

3. A gray iron casting containing appreciable amounts of carbon in flakeform and having a metallic matrix consisting predominately of pearliteto the substantial exclusion of free ferrite and containing as anessential ingredient for such condition an amount of antimony of about0.01% to 0.05%.

4. A gray iron casting containing appreciable amounts of carbon in flakeform and having as an essential constituent a small amount of antimonyof the order of 0.01% to 0.10%, said casting in its final form beingcharacterized by having a metallic matrix of great uniformity consistingpredominantly of pearlite to the substantial exclusion of free ferrite,said casting having increased hardness compared with the same gray ironmix without antimony.

5. A composition of matter consisting essentially of gray iron cast froma molten mix and having a large preponderance of the carbon in themolten mix separated and distributed through the cast iron as primarygraphite in flake form and with the remaining proportions of carboncombined as iron carbide uniformly admixed with ferrite to formessentially all pearlitic iron and containing antimony included in themolten mix and in an amount from 0.01% to 0.1% and less than wouldinhibit formation of primary graphitic carbon during the cooling of themolten iron mix to normal room temperatures.

6. A composition of matter consisting essentially of gray iron cast froma molten mix to separate a large preponderance of the carbon in themolten mix during transition of the molten mix to the solid state asprimary graphite in flake form distributed through the solidified ironand the remainder of the carbon in the cast com position combined asiron carbide and uniformly admixed with ferrite to form essentially allpearlitic iron and containing antimony included in the molten mix and inan amount from 0.01 to 0.1% and less than would inhibit formation ofprimary graphitic carbon during the cooling of the molten iron mix tonormal room temperatures, said solidified iron material having thepearlite distributed essentially uniformly throughout and thecomposition being substantially free from chilled edges or sections andfrom non-pearlitic regions.

LESTER C. CROME.

REFERENCES CllED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,973,263 Mitchell et al Sept.11, 1934 2,253,502 Boegehold Aug. ,26, 1941 2,378,548 Gregg June 19,1945 FOREIGN PATENTS Number Country Date 142,090 Austria June 11, 1935809,815 France Mar. 10, 1937

1. A GRAY IRON CASTING OF SUCH COMPOSITION, SIZE AND CONFIGURATION ASNORMALLY TO BE SUBSTANTIALLY FREE OF CHILLDED HARD REGIONS DIFFICULT TOMACHINE SATISFACTORILY AND TO HAVE A BRINELL HARDNESS OF THE ORDER OF179-200, SAID CASTING CONTAINING APPRECIABLE AMOUNTS OF CARBON IN FLAKEFORM AND HAVING A METALLIC MATRIX OF GREAT UNIFORMITY CONSISTINGPREDOMINATELY OF PEARLITE TO THE SUBSTANTIAL EXCLUSION OF FREE FERRITEAND CONTAINING AS AN ESSENTIAL CONSTITUENT A SMALL AMOUNT OF ANTIMONY OFTHE ORDER OF 0.01% TO 0.10%, SAID CASTING BEING SUBSTANTIALLY FREE OFCHILLED HARD REGIONS, AND EXHIBITING A BRINELL HARDNESS OF THE ORDER OF200-235.